The present disclosure relates to battery packs for automotive vehicles. More particularly, the present disclosure relates to battery cooling apparatus using air to cool battery packs having at least one stacked array of rechargeable battery cells.
Electric vehicles, including hybrid electric vehicles, have electric motors for propelling the vehicles along roadways, for example, and these electric motors typically rely upon onboard rechargeable batteries as their energy source. Battery packs having a fairly large number of individual rechargeable battery cells are frequently used with such vehicles. An example of a battery cell that is used in electric vehicles is a lithium ion battery cell. When recharging and when discharging to provide power to the electric motors of electric vehicles, the battery cells generate heat that needs to be removed in order to maintain the battery cells below their maximum allowable temperatures so that the battery cells are not damaged or destroyed by the heat. When removing heat from battery packs, it is desirable but not necessary to have the faces of each of the battery cells maintained at a fairly uniform temperature.
Some electric vehicles may use liquid cooling systems to cool their battery packs. For example, liquid cooling systems using approximately 50% ethylene glycol or other similar cooling fluids in water have been developed. The cooling fluid is pumped or otherwise moved passed the battery cells to remove the heat from the cells. The benefit of liquid cooling systems is that the volumetric heat capacity of the liquid allows tight control of temperature uniformity. However, liquid cooling systems are heavy, costly, take up a lot of space, and are prone to developing fluid leaks, especially if they employ numerous fluid connections.
Using air to cool battery packs, rather than liquid, introduces a host of other concerns. Any cooling media possesses a finite thermal heat capacity per unit of mass and will increase in temperature as it passes by the surface of the heat-generating item to be cooled, such as a battery cell. Air is a low-density cooling medium and can experience high temperature gradients as it passes along a surface to be cooled if there is a poor ratio of air flow to heat absorption. In typical battery pack cooling systems in which air is used as the cooling media, near the inlet, the temperature of the battery cell face is approximately equal to the inlet air temperature and near the outlet, the temperature of the battery cell face is approximately equal to the outlet air temperature. An example of a known air cooling system for a battery pack is shown and described in U.S. Pat. No. 5,015,545. Often with these conventional air cooling designs, the air temperature increases across the face of the battery cell by more than the preferred 3° Celsius for a lithium ion battery, for example. Accordingly, there is a need for an improved air cooled battery pack apparatus.